1. Field of Invention
The invention relates to a holding container equipped with an inner container surrounded by a layer of thermally treated material for the purpose of inducing and maintaining a desired thermal condition of the contents placed within the inner container.
2. Description of the Prior Art
It is generally held as desirable to consume beverages such as beer, soft drinks, and fruit juices, when they are cold. Placing ice cubes in the drink is the common way of doing this. While reasonably effective for keeping the drink cook, the melting ice causes the drink to lose carbonation, and become watery, destroying the quality of the beverage.
Preparing and serving ice cubes is messy, and bothersome, and backlog of them takes up valuable freezer space. Though automatic ice cube makers reduce some of the hassle of preparing ice, they are very expensive, and require special installation and routine servicing. Ice made in automatic ice cube makers, can become contaminated with chemical and mineral impurities that accumulate in the water supply lines. In addition to imparting a foul taste, these contaminants are capable of causing severe illness in persons that consume beverages containing contaminated ice. As indicated in the instruction manuals that come with automatic ice makers, routine servicing must be done in order to avoid this very unpleasant possibility. In addition to this extra inconvenience, the knowledge that increasing amounts of pollutants are accumulating in one's supply of beverage ice cannot be said to add one's drinking pleasure!
Another disadvantage of ice is that it absorbs odors from other foods stored in the freezer. These odors also imparting a foul taste to the ice and hence, the beverage in which they are used. This often results in the need to discard the ice, which is wasteful of water, energy, and one's time.
The quantity of ice commonly used during beverage consumption is far more than is actually needed to cool the drink. The usual practice of discarding ice after the drink is finished, wastes perhaps as much water and energy as is used in the drink itself. Though this quantity seems small on a unit basis, it is the way in which over 300 million beverage are consumed each day in the U.S. alone!
Though ice cubes are inconvenient, messy, destructive to the beverage quality, wasteful of water and energy resources, they prevail as the dominant way of cooling beverages during their consumption.
The aim of the prior art has been to produce a drinking tumbler or similar device, that is equipped with its own refrigerant, that cools the beverage, without the use of ice, with the promise of greater convenience, and improved beverage quality. In spite of these alleged advantages over the conventional ice cube method, many factors have hampered widespread success of beverage coolers of the prior art. Bulk, expense, unattractiveness, discomfort in use, short product life, along with poor cooling performance, have weighted heavily against the commercial success of these devices.
The basic design of these beverage cooling devices has changed very little in the 60 years since their introduction by Mock, U.S. Pat. No. 1,771,186 (1928). An inner container, or "cup", holds the drink while it is being consumed. The inner container is enclosed within a larger outer container. The compartment between the containers, is filled with a water based refrigerant, and hermetically sealed. The beverage is cooled, as heat is absorbed by the refrigerant, through the walls of the inner container. The refrigerant, usually a plastic "gel", or water solution containing propylene glycol, alcohol, or various minerals salts, is frozen by placing the beverage cooler into the freezer compartment of a refrigerator.
When frozen, the refrigerant, being mostly water, gains about 10% in additional volume. Because of this extra volume, the compartment holding the refrigerant is filled to only 75% to 90% of its capacity, as rupture of the walls results from freezing one that is completely full. The remaining 10% to 25% of the compartment, contains a void or air space, often referred to as an "expansion air space". This expansion air space is intended to allow a place for the expansion volume of the refrigerant.
The position of this "expansion air space" within the compartment holding the refrigerant, is critical to the operation of several prior art beverage coolers. The designs of Mock, U.S. Pat. No. 1,771,186 (1928), Stoner, U.S. Pat. Nos. 3,205,677, 3,205,678 (1965) and 3,302,428 (1967) and Paquin, U.S. Pat. No. 3,360,957 (1968), and others, required the unit to be placed upside down when frozen in the refrigerator freezer. Failure to invert the unit reduces cooling performance as the frozen mass of refrigerant is inclined to slide out of contact with the inner container as the refrigerant begins to melt, disconnecting the refrigerant from thermal contact with the beverage. Another reason is that freezing the unit in the upright position places the expansion air space in the upper portion of the compartment, depriving the more important upper portion of the beverage of refrigerant for cooling. This condition gets progressively worse as the refrigerant melts. The melted refrigerant, having a smaller volume than when frozen, settles to the bottom of the compartment, leaving the upper portion of the inner container out of contact with the refrigerant. The upper portion of the beverage is at more of a disadvantage than any other region of the beverage, having the lowest amount of contact area with the refrigerant, and the greatest amount of exposure to heat from the environment. The temperature of the beverage in this area rises rapidly, once the refrigerant loses contact with the adjoining wall of the inner container.
The condition just described, is further worsened when the upper portion of the inner container is tapered outward, a common practice of the prior art. The taper reduces the volume of the upper region of the compartment, and hence the amount of refrigerant available for cooling that portion of the beverage. Because the volume of this area is so much less by comparison to the bottom region, a loss of just 10% in the volume of the refrigerant may cause a third or more of the upper portion of the inner container to be uncovered! The taper provides still more disadvantages, by enlarging the opening of the inner container. This exposes an even greater amount of the beverage to heat contamination from the environment than the straight sided inner container described earlier, while exaggerating the loss of refrigerant available to this area. A beverage cooler of this configuration would be very difficult, if not impossible to maintain at a consistant temperature throughout.
Another reason prior art beverage coolers are frozen upside down is to position the expansion air space between the bottoms of the inner and outer containers. This is done to prevent fracture and bowing of the bottoms when the refrigerant expands. If the unit is placed right side up in the refrigerant freezer, the refrigerant immediately fills the space between the bottoms of the containers. This puts the expansion air space at the other end of the compartment, depriving the area between the bottom of the containers of space for the extra volume of refrigerant to expand. The result, if not a wall fracture, is an excessive amount of bowing of the bottom of the container, to the extent of causing the unit to stand lopsided. Moore et al., U.S. Pat. No. 4,163,374 (1979), observed these forces to be sufficient to cause the retaining ring, that held his entire unit together, to disengage from the outer container to which it was attached. This occurred in spite of high elasticity of both the styrofoam outer container, and the flexible plastic retaining ring! Forces like these, imposed on container walls made of more rigid materials, such as metal or glass, are sufficient to cause fracture of the walls, and permanent damage to the unit. It then becomes necessary to increase the wall thickness in order to resist the forces imposed on them. Thicker container walls, on the other hand, are undesirable in that they add bulk, material cost, and greatly slow the cooling speed of the unit, particularly if constructed of low conductivity materials such as glass or plastic.
Compression of the expansion air space is another contributor to stresses imposed upon the container walls. This occurs when the refrigerant expands to its larger frozen volume.
For example, a typical prior art refrigerant compartment filled to 90% capacity has an expansion air space equal to the remaining 10% of the volume of the compartment. As previously stated, the refrigerant gains about 10% volume when frozen, resulting in an expanded volume that occupies about 99% of the volume of the compartment. This leaves only 1% of the compartment available to contain the expansion air space. While the expansion air space will lose about 1/6th of its volume when reduced to 0.degree. F. in the freezer, that leaves a volume that would normally occupy 8.3% of the compartment compressed into a space equal to about 1%! This results in a buildup of air pressure within the compartment that threatens the hermetic condition of the compartment. It may also cause the walls of thinner walled units to bow placing limits on the thinness of the walls that would not otherwise apply.
Compression of the expansion air space may also occur during the dry cycle of an automatic dishwasher. At around 175.degree. F., a typical prior art beverage cooler with a 10% expansion air space will see about a 40% compression of the air space. This degree of compression is not as great as is experienced from the expanded refrigerant, but in combination with heat and moisture it may cause permanent warpage to plastic walled units.
Changes of elevation also affect compression of the expansion air space. Within habitable elevations, say from sea level to around 5,000 feet, the expansion air space will undergo compression to a similar degree to what may be expected in the dry heat cycle of an automatic dishwasher.
For example, a unit manufactured in Los Angeles, and shipped to Denver, or Albuquerque, may experience outward bowing of the compartment walls upon arrival. The buildup of air pressure may also be sufficient to rupture the hermetic seal, resulting in leakage of the refrigerant out of the compartment.
Conversely, a similar unit manufactured in Denver or Albuquerque, and shipped to Los Angeles may find the walls of the beverage cooler "caved in" upon arrival. The air pressure within the compartment resulting from the difference in air density between the two elevations may also be sufficient to rupture the hermetic seal to the destruction of the unit.
Still another inherent disadvantage of using the expansion air space, is the need for precise measuring of the refrigerant during manufacture of the beverage cooler. Improper metering of the refrigerant can have drastic consequences on the performance of the unit. Too little refrigerant reduces available cooling power, and exaggerates loss of contact with the upper portion of the inner container as already described. Too much refrigerant may cause permanent damage to the unit, should the expanded volume of the refrigerant exceed the volume of the expansion air space.
Another prior art strategy used for dealing with the problems of the expanded refrigerant , is to shift the extra volume into the wall of the outer container. Used in combination with an expansion air space, Stoner, U.S. Pat. No. 3,205,678 (1965), recommends the use of plastic inner and outer containers, with a thicker inner container wall. The extra rigidity of the thicker inner container wall is intended to resist buckling from the expanded refrigerant, causing it to shift outwardly into the outer wall. The thinner, more flexible outer wall is allowed to bow in response to the force of the expanded refrigerant.
The consequence of adding to the wall thickness of the inner container, is that it greatly slows the cooling affect upon the beverage. This is most dramatic in containers made of low thermal conductors such as plastic. Even slight increases in the wall thickness of inner containers made of plastic has a profound affect upon the cooling speed.
The problem with using a thinner walled outer container, is that it tends to concentrate the expansion volume of the refrigerant in toward the inner container, contrary to the desired goal. The higher thermal conductivity of the thinner outer container wall, coupled with its larger surface area and exterior exposure, cause the refrigerant to freeze from the outside in. This pushes the expansion volume of the refrigerant in toward the inner container, which must resist this force until it can be deflected outwardly again. Having to resist this concentration of force adds further to the thickness requirement of the inner container and hence, the slowing of the cooling speed of the beverage cooler.
A similar approach, recommended by Moore, et al., U.S. Pat. Nos. 4,163,374 (1979), 4,299,100 (1981), 4,378,625 (1983), uses a styrofoam outer container to absorb the expansion volume of the frozen refrigerant. Though styrofoam is initially resilient, with repeated use it quickly loses its ability to recover from compression. The rigid structure breaks down, resulting in weakened walls that crack and leak refrigerant. Styrofoam is too fragile to join other materials to with any degree of reliability in the strength of the connection. Disengagement of component connections could easily occur as a result of uneven distribution of the refrigerant between the containers to the destruction of the unit. The inward and outward flexing action in response to the freezing and thawing of the refrigerant also threatens the integrity of the connections.
The high thermal insulative properties of styrofoam prevent a significant amount of thermal energy from traveling out of the refrigerant through the outer container wall. This greatly increases the amount of time required to prepare the unit for use in the refrigerator freezer, by perhaps a factor of 5.
The increased probability of wall fractures and leaks, makes the styrofoam outer container design dependent on the use of plastic "gel" refrigerants. Gel refrigerants have the disadvantage of being more expensive, more toxic, less durable, and have a higher coefficient of expansion upon freezing than most liquid refrigerants. Gels are also more difficult to load into the beverage cooler, and require special manufacturing processes and component design features. A lot of prior art is devoted to solving the problems related to loading the gel into the beverage cooler.
The all metal, inner and outer container beverage coolers of the prior art also have a several inherent flaws. The designs of Thomsen, U.S. Pat. No. 1,369,367 (1921), Mock U.S. Pat. No. 1,771,186 (1928), Munters U.S. Pat. No. 2,039,736 (1931), Flannery U.S. Pat. No. 3,161,031 (1964), Stoner U.S. Pat. No. 3,205,677 (1965), Coleman U.S. Pat. No. 3,394,562 (1967), and Canosa U.S. Pat. No. 3,680,330, (1972), ect., all recommend the use of metal inner and outer containers.
Metal containers in general, are heavier, and more expensive to produce than those made of plastic. Aluminum is often the preferred metal of the prior art, being relatively lightweight, corrosion resistant, and having a high coefficient of thermal conductivity.
The problems inherent in the all metal beverage cooler design, are derived mainly from the outer container. Being much larger than the inner container, the outer container represents the major portion of the weight and cost of the unit. Its largest surface area, coupled with its high thermal conductivity and exterior exposure, attract heat from the environment, even when fitted with insulation. This creates a power drain on the refrigerant.
Another area of thermal inefficiency occurs around the top horizontal portions connecting the two containers. The high thermal conductivity of the metal, creates a thermal exchange interaction between the containers, to bring them into thermal equallibrium with each other. This condition is undesirable, as the inner container in contact with the beverage, becomes warmer, while the outer container, most vulnerable to heat contamination from the environment, becomes warmer, attracting still more heat. In addition to causing a warmer beverage, it causes the beverage cooler to lose power faster.
The relationship between the proportions of the inner container, and the speed and uniformity of cooling of the beverage, are factors hitherto unappreciated by the prior art. Tub shaped inner containers, typically used by the prior art, produce a beverage cooler that is slower and less uniform in cooling than one with an elongated inner container.
A tub shaped container, generally has a height equal to less than about 2 diameters. The large diameter relative to the height, give the container a "tub-like" appearance, hence the name. While generally lacking specific dimensions, the drawing figures shown in the following U.S. patents; Devlin U.S. Pat. No. 3,715,895 (1973), Canosa U.S. Pat. No. 3,680,330 (1972), Coleman U.S. Pat. No. 3,394,562 (1968), Paquin U.S. Pat. No. 3,360,957 (1968), Stoner U.S. Pat. No. 3,205,677 (1965), Flannery U.S. Pat. No. 3,161,031, (1964), show tub shaped inner containers.
The inherent disadvantages of having a tub shaped inner container, is that, due to the natural configuration, a great deal of refrigerant is concentrated around the bottom of the container, furthest away from the more critical upper portion of the container. The larger diameter opening exposes more of the beverage to heat contamination from the room environment, while increasing the distance the heat must travel to go from the beverage into the refrigerant. The loss of contact between the refrigerant, and the upper portion of the inner container is greater, especially when it is tapered outward, as described earlier in this section.
In addition to taking longer to induce cooling of the beverage, the surface of the beverage tends to be warmer than the lower region in beverage coolers with tub shaped inner containers. They lose power sooner, and require more refrigerant in order to produce and maintain slush.
Devlin, U.S. Pat. No. 3,715,895 (1973), recommends a refrigerant volume equal to up to 3 times the volume of the beverage. In spite of this enormous volume of refrigerant, it still took up to ten minutes to produce a slush in his mug, even using prerefrigerated ingredients! In addition to being slow, a 355 ml. (12 ounce) capacity mug of this description would weigh at least 1.5 kilos (3 pounds)! That is more than twice the weight of an ordinary glass beer mug!
The performance of a poorly designed beverage cooler may sometimes be improved by overwhelming it with a very large mass of refrigerant, like the one just described. The added bulk, however, produces a unit that is heavier, and less attractive, in addition to being more expensive.
The cooling speed of a prior art beverage cooler could be increased by lowering the freezing point of the refrigerant, but it also reduces the enthalpy (heat content) of the refrigerant. A refrigerant with a lower freezing point takes longer to freeze, and loses power sooner than one with a higher freezing point. This diminishes the overall performance of the beverage cooler in ways that can only be compensated for by again increasing the volume of the refrigerant, an undesirable alternative.
As can be seen in the many examples sighted above, several problems continue to plaque beverage cooling devices of the prior art. We see how the so called solutions to these problems have often given rise to new problems, unrecognized and unsolved by the prior art.
These factors add up to a variety of poorly performing beverage cooling devices, that after more than 60 years of development, have failed to produce a commercially significant design, that offers a viable alternative to the common prepared ice method of beverage cooling. Dispite the fact that ice cubes are messy, inconvenient, wasteful, and destructive to beverage quality, they remain the only method, generally available to the public, for cooling beverages during consumption.